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Analysis of Retinoid X Receptor (RXR) Homodimerization Driven by RXR Ligands Using Yeast Two-Hybrid

Description

Bexarotene (Targretin®) is an FDA approved drug used to treat cutaneous T-cell lymphoma (CTCL), as well as off-label treatments for various cancers and neurodegenerative diseases. Previous research has indicated that bexarotene has a specific affinity for retinoid X receptors

Bexarotene (Targretin®) is an FDA approved drug used to treat cutaneous T-cell lymphoma (CTCL), as well as off-label treatments for various cancers and neurodegenerative diseases. Previous research has indicated that bexarotene has a specific affinity for retinoid X receptors (RXR), which allows bexarotene to act as a ligand-activated-transcription factor and in return control cell differentiation and proliferation. Bexarotene targets RXR homodimerization to drive transcription of tumor suppressing genes; however, adverse reactions occur simultaneously when bound to other nuclear receptors. In this study, we used novel bexarotene analogs throughout 5 iterations synthesized in the laboratory of Dr. Wagner to test for their potency and ability to bind RXR. The aim of our study is to quantitatively measure RXR homodimerization driven by bexarotene analogs using a yeast two-hybrid system. Our results suggests there to be several compounds with higher protein activity than bexarotene, particularly in generations 3.0 and 5.0. This higher affinity for RXR homodimers may help scientists identify a compound that will minimize adverse effects and toxicity of bexarotene and serve as a better cancer treatment alternative.

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Date Created
2015-05

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Characterization of Second and Third Generation, Novel RXR Selction Agonists for the Treatment of Cutaneous T-Cell Lymphoma

Description

Bexarotene is a commercially produced drug commonly known as Targetin presecribed to treat cutaneous T-cell lymphoma (CTCL). Bex mimics the actions of natural 9-cis retinoic acid in the body, which are derived from Vitamin A in the diet and boost

Bexarotene is a commercially produced drug commonly known as Targetin presecribed to treat cutaneous T-cell lymphoma (CTCL). Bex mimics the actions of natural 9-cis retinoic acid in the body, which are derived from Vitamin A in the diet and boost the immune system. Bex has been shown to be effective in the treatment of multiple types of cancer, including lung cancer. However, the disadvantages of using Bex include increased instances of hypothyroidism and excessive concentrations of blood triglycerides. If an analog of Bex can be developed which retains high affinity RXR binding similar to the 9-cis retinoic acid while exhibiting less interference for heterodimerization pathways, it would be of great clinical significance in improving the quality of life for patients with CTCL. This thesis will detail the biological profiling of additional novel (Generation Two) analogs, which are currently in submission for publication, as well as that of Generation Three analogs. The results from these studies reveal that specific alterations in the core structure of the Bex "parent" compound structure can have dramatic effects in modifying the biological activity of RXR agonists.

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Date Created
2012-05

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Luminometric Analysis of Yeast Calcium Channel Homeostasis Following Hypotonic Shock

Description

Calcium is the only ion capable of triggering electrical and chemical reactions in cells which are part of essential biomolecular processes, such as gene transcription and ion flux. Calcium homeostasis, the control of concentration levels, is therefore crucial for the

Calcium is the only ion capable of triggering electrical and chemical reactions in cells which are part of essential biomolecular processes, such as gene transcription and ion flux. Calcium homeostasis, the control of concentration levels, is therefore crucial for the proper functioning of cells. For example, cardiomyocytes, the cells that form cardiac muscle, rely on calcium transfer process to produce muscle contraction.
The purpose of this work is to study aspects of calcium homeostasis in the model organism Saccharomyces cerevisiae, common yeast. Using luminometric techniques, the response of the yeast was monitored against a set of changes in the environment calcium abundance. The results indicate a complex response as both increase and decreases of external calcium induce elevations in cytosolic calcium concentrations.
Calcium is transferred across compartments by means of channels. In Saccharomyces cerevisiae, many of them have been identified; Cch1p-Mid1p, Vcx1p, Pmc1p, Pmr1p, and Yvc1p. Their participation in calcium homeostasis is well established. Observations of cytosolic calcium increase after a hypertonic shock are mainly associated with influx of ions from the environment though the Cch1p-Mid1p. This process is generally considered as driven by calcium concentration gradients. However, recent studies have suggested that the plasma membrane channel, Cch1p-Mid1p, may possess more sophisticated regulation and sensory mechanisms. The results of our experiments support these ideas.
We carried out experiments that subjected yeast to multiple shocks: a hypertonic shock followed by either a second hypertonic shock, a hypotonic shock, or a yeast dilution pulse where the solution volume increases by the calcium concentration has only a small change. The cytosolic calcium concentration of a yeast population was monitored via luminometry.
The main result of this study is the observation of an unexpected response to the combination of hypertonic and hypotonic shocks. In this case it was observed that the cytosolic calcium concentration increased after both shocks. This indicates that cytosolic calcium increases are not solely driven by the presence of concentration gradients. The response after the hypotonic pulse arises from more complex mechanisms that may include sensor activity at the membrane channels and the release of calcium from internal storages.

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Created

Date Created
2020-05

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Design and Engineering of Synthetic Gene Networks

Description

Synthetic gene networks have evolved from simple proof-of-concept circuits to

complex therapy-oriented networks over the past fifteen years. This advancement has

greatly facilitated expansion of the emerging field of synthetic biology. Multistability is a

mechanism that cells use to achieve a discrete number

Synthetic gene networks have evolved from simple proof-of-concept circuits to

complex therapy-oriented networks over the past fifteen years. This advancement has

greatly facilitated expansion of the emerging field of synthetic biology. Multistability is a

mechanism that cells use to achieve a discrete number of mutually exclusive states in

response to environmental inputs. However, complex contextual connections of gene

regulatory networks in natural settings often impede the experimental establishment of

the function and dynamics of each specific gene network.

In this work, diverse synthetic gene networks are rationally designed and

constructed using well-characterized biological components to approach the cell fate

determination and state transition dynamics in multistable systems. Results show that

unimodality and bimodality and trimodality can be achieved through manipulation of the

signal and promoter crosstalk in quorum-sensing systems, which enables bacterial cells to

communicate with each other.

Moreover, a synthetic quadrastable circuit is also built and experimentally

demonstrated to have four stable steady states. Experiments, guided by mathematical

modeling predictions, reveal that sequential inductions generate distinct cell fates by

changing the landscape in sequence and hence navigating cells to different final states.

Circuit function depends on the specific protein expression levels in the circuit.

We then establish a protein expression predictor taking into account adjacent

transcriptional regions’ features through construction of ~120 synthetic gene circuits

(operons) in Escherichia coli. The predictor’s utility is further demonstrated in evaluating genes’ relative expression levels in construction of logic gates and tuning gene expressions and nonlinear dynamics of bistable gene networks.

These combined results illustrate applications of synthetic gene networks to

understand the cell fate determination and state transition dynamics in multistable

systems. A protein-expression predictor is also developed to evaluate and tune circuit

dynamics.

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Created

Date Created
2017